In the early years of prosthetic surgery of the hip-joint, attempts were made to replace only the joint head with an implant held by a straight stem, which was held by the femoral neck and the spongy substance of the adjoining epiphysis of the femur. It was found that this arrangement was inadequate for transmitting the forces to the femur. Hip prostheses are therfore mostly used whose stem reaches into the diaphysis of the bone (FR-A-2,636,837, U.S. Pat. No. 5,413,610, GB-A-2,069,340; EP-A-477,113, FR-A-2,706,283, EP-A-711,534, FR-A-2,629,707, FR-A-2,429,010). To obtain sufficient access for this, the femoral neck is completely resected. In recent years, hip prostheses have been proposed which allow the femoral neck to be preserved. The resection is carried out immediately below the joint head (EP-A-666,069, col. 2, l. 47; EP-A-579,868, col. 8, l. 51; WO 87/00033, p. 6, col. 19). A collar-like neck bearing is provided which is supported on the resection surface of the femoral neck. The distance of the support surface of the neck bearing from the center of the joint head of the prosthesis is unchangeable because variations are ruled out as a result of the resection immediately below the joint head. By contrast, in the case of conventionally implanted hip prostheses, it is known (FR-A-2,429,010, FR-A-2,629,707, U.S. Pat. No. 5,413,610, FR-A-2,636,837) to keep-in stock different neck lengths of the prosthesis for the purpose of compensating for different neck lengths of the bone that is to be replaced.